1. Field of the Invention
The present invention relates to a valve control device fop an internal combustion engine.
2. Description of the Prior Art
For internal combustion engines, it is a well known technique to rest cylinders by stopping actuation of suction (intake) and exhaust valves and fuel supply, or to vary valve timing and valve strokes, in order to lower fuel consumption and enhance output. In general, suction and exhaust valves fop opening and closing suction and exhaust ports which ape provided in a combustion chamber of an engine are controlled to be opened and closed by a mechanism in which one end of a rocker arm swinging around a rocker shaft contacts a lope end of a valve stem of each valve, while the other end of the rocker arm is connected to a pushrod via an adjuster, and the pushrod is combined with a cam through a tappet, and often by a mechanism in which the other end of the rocker arm is combined with a cam, or a direct type mechanism in which the valve stem is in direct contact with the cam via a lifter. Thus, a lot of mechanisms for operating suction and exhaust valves have been proposed so far. Further, in order to rest cylinders by keeping suction and exhaust valves closed, improvements have been made to a lifter disposed between the aforementioned rocker arm or cam, and the fore end of the valve stem. An example of the improvements is disclosed in Japanese Examined Utility Model Publication No. 7526/1991.
In this publication, a plunger having an axis perpendicular to an axial direction of a valve stem is provided in a lifter. The plunger has a receiving surface which can contact a fore end portion of the valve stem, and an idle bore for receiving the fore end portion of the stem. When hydraulic pressure is applied on one end of the plunger, the plunger slidably moves in the lifter against the urging force of a spring provided at the other end of the plunger, thereby bringing the fore end portion of the valve stem which has been in contact with the receiving surface to enter the idle bore. When the fore end portion of the valve stem enters the idle bore, reciprocating motion caused by the cam is not transmitted to the valve stem, only to make the fore end portion of the valve stem go in and out of the idle bore of the plunger and leave the suction or exhaust valve closed. When hydraulic pressure which has been applied on the one end of the plunger is relieved and the lifter comes to the upper limit position (in this position, the fore end portion of the stem is out of the idle bore), the spring provided at the other end of the plunger urges the plunger to the initial position, i.e., the position at which the receiving surface of the plunger contacts the fore end portion of the valve stem, thereby allowing regular operations of the suction or exhaust valve.
In this publication, however, the receiving surface of the plunger in the lifter contacts the fore end portion of the valve stem by the force of the spring fixed on the valve stem. In this case, since the line of action of the spring force of the valve stem is perpendicular to the axial direction of the plunger, the plunger receives force to deviate the axis of the plunger, and moreover, transmits this force to the lifter via the outer circumferential surface of the plunger. Since the transmission of this force produces unbalanced wear on the receiving surface and the outer circumferential surface of the plunger and deviates the axis of the plunger, the plunger does not move smoothly, and the valve change-over operation offers a problem of reliability.